1. Field of the Invention
The present invention concerns a positive active material for nickel electrodes for alkaline electrolyte storage batteries. It also extends to the method of preparing the active material and to its use in the manufacture of the electrode
2. Description of the Prior Art
Most recent applications of alkaline electrolyte storage batteries oblige the user to charge the batteries at temperatures higher than room temperature. This is the case when the storage batteries are used in vehicle traction, for example. When the charging temperature is in the order of 40.degree. C. to 60.degree. C., the efficiency of charging the positive electrode is poor because the oxygen release excess voltage at the end of charge is low.
U.S. Pat. No. 5,466,543 describes a paste type electrode for alkaline storage batteries adapted to operate over a wide range of temperatures. The paste contains an active material and at least one compound of yttrium, indium, antimony, barium, beryllium and at least one compound of cobalt or calcium.
European patent application 0 634 804 proposes a paste comprising a mixture of active materials consisting mainly of nickel hydroxide and containing at least one element selected from cobalt, cobalt hydroxide, cobalt oxide, carbon and nickel and a powder compound of at least one element chosen from Ca, Sr, Ba, Cu, Ag and Y.
The efficiency obtained with such electrodes is still insufficient for some applications. These poor results are associated with unsuitable distribution of the substances in the paste and the formation of lumps which renders some of the additives ineffective.